1. Field of the Invention
The present invention relates generally to apparatus and methods for separating cellular components from biological fluids and, more particularly, to the design and use of a centrifugal rotor which is capable of continuously separating plasma from an applied volume of whole blood as the rotor is spun.
Analytical testing of biological fluids frequently requires that cellular components be separated from the fluid in order to provide a red blood cell-free fluid fraction for analysis. For example, many blood tests require removal of blood cells so that analysis can be performed on the remaining blood plasma. A common method for achieving such cellular removal employs a analytical rotor where the relatively dense cellular components are centrifugally separated from the less dense blood plasma. Frequently, the resulting blood plasma undergoes a detection reaction, e.g., an immunological or enzymatic reaction, and subsequent optical analysis within the analytical rotor.
Heretofore, most analytical rotors for separating cellular components from biological fluids have been designed for batch-type separation. In batch separation, a discrete volume of the biological fluid is applied to the rotor, and the rotor then spun to separate the entire applied fluid volume into a cellular fraction and a cell-free fluid fraction prior to performing any reaction or optical analysis. Usually, the cell-free fluid fraction will first be collected within a collection compartment or chamber and only after the entire volume is collected, the fraction will be transferred to a separate region within the rotor in order to perform a reaction or other analytic procedure.
The need to completely separate cellular components from the biological fluid prior to analysis, however, is disadvantageous in several respects. First, the initial separation step can be time-consuming and significantly delay the initiation of subsequent steps in the analysis, e.g., reaction with immunological reagent(s) and/or optical examination. Second, the need to transfer cell-free fluid within the rotor after the initial separation is complete usually requires additional step(s) in the analytical protocol. Such additional step(s) complicate the protocol and further increase the time required to perform the analysis. In automated testing systems, even small time delays and minor complications of the analytical protocol can greatly decrease the efficiency of the test being performed.
For these reasons, it would be desirable to provide improved analytical rotors and methods for separating cellular components from biological fluids, where the separation can be achieved continuously and simultaneously with transfer of cell-free fluid to a separate region within the rotor wherein the fluid can be subjected to an analytical reaction or optical examination, or both. In particular, it would be desirable to be able to initiate transfer of the cell-free fluid into a collection chamber or chambers where analytical reactions and/or analyses can begin even while the rotor continues to spin and before the entire biological fluid volume has been separated. It would further be desirable to be able to combine and mix diluents with the biological fluid as a part of the separation protocol.
2. Description of the Background Art
U.S. Pat. No. 4,708,712, describes a rotor intended for continuous plasma separation for use in therapeutic procedures, such as plasmapheresis. The rotor includes an eccentrically disposed channel which receives blood through an inlet port. The channel is positioned so that it has a decreasing radius relative to the axis of rotation in the clockwise direction from the inlet port and an increasing radius in the counterclockwise direction. Whole blood entering the channel from the inlet will separate into a lighter fraction (including plasma and platelets) which flows in the clockwise direction in a heavier fraction (including plasma and blood cells) which flows in the counterclockwise direction. The blood cells are collected in a dam region which is located in a maximum radial distance from the axis. U.S. Pat. Nos. 4,419,089 and 4,356,958, disclose the concept of using eccentric or spiral channels for separating blood cells from plasma by centrifugation. U.S. Pat. No. 3,899,296, discloses a separation chamber within an analytical rotor, where plasma is removed by aspiration rather than by continued centrifugation. U.S. Pat. No. 4,894,204, discloses the use of a siphon structure to hold liquid in a rotor receptacle. See also U.S. Pat. Nos. 3,901,658; 4,279,862; 4,284,602; 4,314,968; 4,350,283; 4,381,072; 4,463,097; 4,680,025; 4,776,964; 4,847,205; and 4,876,203, which relate to the construction and use of various devices for separating cells from blood and other biological fluids.